Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session GI2b: Plasma Simulations |
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Chair: Bruce Langdon, Lawrence Livermore National Laboratory Room: Adam's Mark Hotel Plaza Ballroom EF |
Tuesday, October 25, 2005 3:00PM - 3:30PM |
GI2b.00001: Kinetic Approach to microscopic-macroscopic coupling in fusion plasmas Invited Speaker: The need to handle the coupling between microscopic and macroscopic processes is an outstanding problem in plasma physics. The wide difference in mass between electrons and ions and the great change in time and space scales between large scale magnetohydrodynamic processes and small scale kinetic effects pose a great challenge to the simulation of plasma physics problems. The traditional approach has been to try to derive reduced models of the full first principles physics model, considering only the scales of interest. The approach decouples small scales and large scales and uses different methods for each. The classic example is anomalous resistivity that is used as a tool to summarize in resistive MHD models the presence of kinetic microinstabilities. We discuss an alternative approach [1], the use of the implicit kinetic PIC model to resolve all scales at the kinetic level. The approach relies on numerical methods that can effectively average the smallest scales within a correct kinetic treatment while focusing on large-scale structures. It is worth remarking that the approach is different from the gyrokinetic approach that relies on a mathematical formulation of the equations that eliminates the smallest scales. Our approach, instead, is valid on all limits and does not eliminate the contribution of any scale. We describe the new approach, its recent successful application to the study of reconnection [2] and its potential application to thermonuclear burning plasmas. \begin{enumerate} \item G. Lapenta, J.U. Brackbill, W.S. Daughton, Phys. Plasmas, 10, 1577, 2003; W. Daughton, G. Lapenta, P. Ricci, Phys. Rev. Lett., 93, 105004, 2004. \item G. Lapenta, Space Sci. Rev., 107, 167, 2003. \end{enumerate} [Preview Abstract] |
Tuesday, October 25, 2005 3:30PM - 4:00PM |
GI2b.00002: A global simulation for laser driven MeV electrons in fast ignition Invited Speaker: A comprehensive examination of the interaction of a picosecond-long ignition pulse with high-density (40 times critical density) pellets using a two- simensional particle-in-cell model is described. The global geometry consists of a 50-diameter pellet surrounded by a corona which is isolated by a vacuum region from the boundary. Due to the significant spread in the transverse momentum of the hot electrons created during the laser-plasma interactions, the electron distribution is only marginally unstable to the Weibel instability. We find that the return current as well as the forward-going hot electron flux contributes to the instability, with the ions playing an important role of neutralizing the space charge. No global current filament coalescence has been observed. We find also that the simulation size and boundary condition can have profound effects on the nonlinear evolution of the filaments. This work is supported by the US DoE through the Fusion Science Center for Extreme States of Matter and Fast Ignition Physics at University of Rochester. [In collaboration with M.A.Tzoufras, J.Tonge, F.S.Tsung and W.B.Mori (UCLA); M.Fiore, R.A.Fonseca and L.O.Silva (IST, Portugal); and J.C.Adam and A.Heron (Ecole Polytechnique, France)] [Preview Abstract] |
Tuesday, October 25, 2005 4:00PM - 4:30PM |
GI2b.00003: Computer models of ion-material and electron-material interactions with application to ion accelerators Invited Speaker: Researchers in heavy-ion-driven high-energy density physics, tokamak physics, high-power microwave physics and accelerator physics are actively studying the interaction between plasmas and walls and between beams and metal surfaces. These interactions result in secondary electron emission, neutral gas desorption, and electron and ion production through impact ionization. A main tool for studying the physics of beam or plasma interaction with surfaces is computer modeling, but many of the main codes in the plasma and beam simulation field do not have sophisticated models of particle-surface interactions. To help fill this need for numerical models of particle-surface interactions, researchers at Tech-X Corporation, Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory and the University of California at Berkeley have developed a set of modules for simulating these interactions. Researchers have benchmarked these modules and used them to help understand results of the High Current Experiment (HCX). We will show the agreement of the numerical routines and experimentally measured results from the HCX that 1.0 MeV potassium ions incident on stainless steel induces the release of roughly six electrons per ion at normal incidence. We also show how self-consistent particle-in-cell simulations using these modules to include effects of secondary electrons produce results that agree more closely with measured currents in the HCX clearing electrodes than simulations without secondary electrons. Researchers have also applied these modules to simulations of high-gradient waveguide breakdown and gas-filled diodes, and we will show results from each. [Preview Abstract] |
Tuesday, October 25, 2005 4:30PM - 5:00PM |
GI2b.00004: Advanced simulations of application plasmas: Comparisons with experiments and validations Invited Speaker: Continuum-fluid and particle-in-cell models are the numerical simulation techniques commonly used for simulating low-temperature plasmas for plasma technology applications. Simulations can often identify research guidelines and propose novel designs leading to performance improvements in different plasma systems. We present an overview of the principles, strengths and limitations of the these. These modeling results are benchmarked by comparing in different plasma systems (capacitively and inductively coupled plasmas) with experimentally measured data and with other numerical results. The potential profile and the electron/ion kinetic information such as electron/ion energy distributions and temperatures are important for understanding the plasma phenomena. Kinetic 1d particle-in-cell/Monte-Carlo-collision and fluid modelings of Ar-oxygen plasma sources are carried out in the wide parameter range. [Preview Abstract] |
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